With the addition of device level Plug and Play (PnP) capabilities it became a great deal easier to setup, configure, and add peripherals to consumer electronic devices and personal computers (PCs). Universal Plug and Play (UPnP™) extends this simplicity to include the entire network, enabling discovery and control of networked devices and services, such as network-attached printers, Internet gateways, and consumer electronics equipment. The UPnP networking protocols are promulgated by the UPnP Forum which is an industry initiative designed to enable simple and robust connectivity among stand-alone devices and PCs from many different vendors.
UPnP is more than just a simple extension of the Plug and Play peripheral model. It is designed to support zero-configuration, “invisible” networking, and automatic discovery for a breadth of device categories from a wide range of vendors. With UPnP, a device can dynamically join a network, obtain an IP (internet protocol) address, convey its capabilities, and learn about the presence and capabilities of other devices—all automatically to thereby facilitate the construction of zero configuration networks. Devices can subsequently communicate with each other directly using peer-to-peer networking to access and share content.
The variety of devices that can benefit from a UPnP enabled network are large and include, for example, intelligent appliances, wireless devices, and PCs of all form factors. The scope of UPnP is large enough to encompass many existing and new applications in such areas as home automation and networking, printing and imaging, audio/video entertainment, kitchen appliances, automobile networks, and mobile device network among others.
UPnP is a distributed, open network architecture that is independent of any particular operating system, programming language, or physical medium. However, UPnP uses standard protocols such as TCP/IP (Transmission Control Protocol/Internet Protocol), HTTP (Hypertext Transfer Protocol) and XML (eXtensible Markup Language), enabling it to seamlessly fit into existing networks. Using such standardized protocols allows UPnP to benefit from interoperability as an inherent feature.
UPnP uses a content directory service that implements a set of functions to provide access to content items (e.g., data files, music, software, pictures, video, games etc.) stored in a content repository on a local UPnP device to remote UPnP devices on the UPnP network. The function of a content directory service is to allow browsing and searching of the content items in the repository. Each content item that is referenced in the content directory service includes various information about that content including the transfer protocols and file formats that the local device can use to transfer the content items to a remote device. As with all UPnP services, remote devices interact with the content directory service using Simple Object Abstraction Protocol (SOAP) calls using HTTP.
After the desired content item has been identified, for example, using a resource or <res> tag in an XML document, the remote device uses the transfer protocol information from the content directory service to match it with the capabilities of a media player in the remote device. Common transfer protocols include HTTP GET and RTSP/RTP (Real Time Streaming Protocol, Real Time Transport protocol), for example. Transferred content is then rendered by the remote device using another UPnP service (the AV Transport Control Service), or a non-UPnP out-of-band protocol, to control the flow of the content (e.g., stop, fast forward, rewind, pause, etc.).
While UPnP performs very satisfactorily in many networking applications, current implementations do not provide users of a UPnP device with file access to content items that are discovered on other UPnP devices connected to a network. That is, a user is limited to only being able to see that a content item exists and perhaps make a request for read-only consumption. No write changes to a discovered content item or file level control of the content item may be implemented in the existing UPnP environment.